This application is based upon and claims the benefit of priority from the prior Japanese Patent Application No. 2000-019524, filed Jan. 28, 2000, the entire contents of which are incorporated herein by reference.
The present invention relates to a method and apparatus for detecting the etching depth capable of detecting the etching depth on the real time basis during the etching of a target object with plasma.
The etching method using plasma is widely employed in various fields such as the manufacturing process of a semiconductor device and the manufacturing process of an LCD substrate. The plasma etching apparatus comprises a lower electrode and an upper electrode arranged in parallel within a process chamber. For performing the plasma etching process, a target object such as a semiconductor wafer is disposed on the lower electrode. Under this condition, a plasma of an etching gas is generated by the discharge between the upper electrode and the lower electrode so as to selectively etch the target object in a predetermined pattern. During the plasma etching process, the state of etching is monitored, as required. An emission spectroscopy technique is proposed as a monitoring method. In this method, however, the time when the specified wavelength of an emission spectrum of the gas generated by the etching is changed is detected as an end point of the etching, making it impossible to know the etching depth changing with time.
A technology for detecting the etching depth is proposed in, for example, Japanese Patent No. 2545948. In this prior art, a window for observation is formed in the upper electrode, and the surface of a semiconductor wafer is irradiated with a monochromatic light such as a laser beam through the observation window from outside the process chamber. The reflected light interfered on the surface of the semiconductor wafer is detected by a detector, and the electric signal converted from the detected light in the detector is subjected to a frequency analysis of interference wave form in a wave form analyzing means by using a maximum entropy method. Then, the etching depth is calculated on the basis of the frequency distribution of the interference wave form, thereby detecting the etching depth on the real time basis. However, in the method using the interference wave form of a laser beam, a periodic distortion in a predetermined phase is unavoidable, and the etching rate is greatly deviated periodically in the distorted portion, resulting in failure to measure and monitor accurately the etching depth.
A first object of the present invention is to provide a method of detecting an etching depth that permits suppressing the influence of the distortion even if there is a distortion of the interference wave form in a predetermined phase so as to detect accurately the etching depth.
Another object of the present invention is to provide a method of detecting an etching depth excellent in time response capability, which permits calculating the etching depth in a short time.
According to a first aspect of the present invention, there is provided a method of detecting an etching depth of a target object, comprising the steps of:
irradiating an etching layer of the target object that is being etched in an etching section with light having at least two components differing from each other in wavelength;
detecting a plurality of interference light components differing from each other in wavelength and having intensity periodically changed by the light components reflected from an upper surface of the etching layer and a surface of the etching section;
applying a frequency analysis to these interference light components so as to obtain the frequency of each of these interference wave forms in which the intensity forms the amplitude;
calculating an etching rate corresponding to each interference wave form by using the frequency of the interference wave form; and
obtaining an etching depth from the etching rate.
According to a second aspect of the present invention, there is provided a method of detecting an etching depth of a target object, comprising the steps of:
irradiating an etching layer of the target object that is being etched in an etching section with a light beam;
detecting an interference light beam having an intensity periodically changed by the light beam reflected from an upper surface of the etching layer and a surface. of the etching section and having an interference wave form in which the intensity forms the amplitude;
determining an approximate formula of the interference light beam;
determining the constants of the approximate formula from the intensity of the interference light beam; and
calculating an etching depth on the basis of the approximate formula, in which the constants have been determined, and the intensity of the interference light beam.
According to a third aspect of the present invention, there is provided a method of detecting an etching depth of a target object, comprising the steps of:
irradiating an etching layer of the target object that is being etched in an etching section with a light beam;
detecting an interference light beam that is periodically changed with the amplitude provided by the intensity caused by the reflected light beam from an upper surface of the etching layer and from a surface of the etching section;
estimating an amplitude of the subsequent interference wave form on the basis of a plurality of extreme values of the interference wave form having an amplitude provided by the intensity of the interference light beam;
calculating a phase on the basis of the interference intensity and amplitude at a certain time; and
calculating an etching depth on the basis of the calculated phrase.
Further, according to a fourth aspect of the present invention, there is provided a method of detecting an etching depth, comprising the steps of:
continuously etching an etching section of an etching layer;
measuring an etching depth of the etching section on the real time basis so as to output a corresponding information;
comparing the output information with an information corresponding to an etching depth set in advance on the real time basis; and
stopping the step of etching when the output information has been found in the comparing step to be equal to the information corresponding to the etching depth set in advance.
Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out hereinafter.